$ cat monk.pl 
#!/usr/bin/perl -w

use strict;

my $x = 'Dwayne Johnson';

print <<XXX;
${x}'s the Sock.
XXX

$ ./monk.pl 
Dwayne Johnson's the Sock.
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Think about it ... say if you wanted to say:
Dwayne Johnson_s the Sock.
Would you say ...

print <<XXX;
$x_s the Sock.
XXX
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... now is $x_s a variable or not? {} and \ tell << that x is a variable.